ANSWER
$3
Or
$4
EXPLANATION
The revenue function is
[tex]r = - 50 {t}^{2} + 300t[/tex]
The cost function is,
C=600-50t
In order to break even, revenue must be equal to cost.
[tex]600 - 50t= -50 {t}^{2} + 300t[/tex]
Group every term on the LHS.
[tex]50 {t}^{2} - 300t - 50t + 600 = 0[/tex]
[tex]50{t}^{2} - 350t + 600 = 0[/tex]
Divide through by 50.
[tex]{t}^{2} - 7t + 12= 0[/tex]
Factor to obtain,
[tex](t - 3)(t - 4) = 0[/tex]
[tex]t = 3 \: or \: t = 4[/tex]